If you live in Los Angeles, you need to stop by The Melrose Trading Post. This vintage flea market is held every Sunday at Fairfax High School. For $3 admission, you get to explore old treasures; clothes, accessories, furniture, music and so on. Most of the things are rather pricey ($40 for a necklace? Ouch!), but you can go there with some friends and enjoy a fresh-squeezed lemonade.
If you're coming here to actually shop, I highly suggest checking out the furniture! You can find yourself some beautiful antique mirrors, vintage luggage (that may double as a nightstand when stacked up), or some crackled-white wooden drawers.
Do always keep in mind: the concept of a flea market is to bargain, don't overpay for what you want! Think about the prices and compare them to brand new items. Also never buy things on the spot, walk around for a bit and come back to your desired item after having the chance to check everything else out.